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Re: 56 kbps modems

>>> People who seemed to know used to say that 'the Shannon limit'
>>> set an absolute upper limit around 40 kbps. Has Shannon been
>>> proven wrong, or what?
>>Well, it all depends on the signal-to-noise ratio. Also, if the noise is
>>not white gaussian the situation can be even better.
>Or it can be worse.  Almost all voice traffic in the US these days,
>either once it gets to your local telephone wire center or maybe before,
>is carried on T1 digital connections, which use 64kbps digital voice -
>it's sampled at 8000 samples/second, A/D converted using a non-linear
>8-bit scale called mu-law (or A-law for Europe), and (for the most common
>framing format) has a signalling channel stego'd onto the LSB of every 6th
>If you knew which the "robbed bit" was, you could get 63 kbps of digital data,
>but since you don't, digital signals are limited to 56kbps since they
>can't trust any of the low bits (analog doesn't lose much from this.)

Couldn't you just 'assume' you knew which bit was 'robbed' and test to see
the result?  If you were wrong, couldn't you advance/retard your clocking
and via a process of elimination sync with the 'robbed bit?


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